The San Francisco company launched with an free iPhone app, a Web site and a roster of high-profile investors that includes actor Ashton Kutcher, noted Silicon Valley investors Ron Conway and Tim Draper, Salesforce CEO Mark Benioff and Dustin Moskovitz, one of Mark Zuckerberg’s Harvard roommates who helped found Facebook.

Path lets people share photos of important moments, but only with a maximum of 50 of their closest friends and family, Morin said in a blog post.

“Think of it as a place for the memories along your path through life,”said Morin, Facebook’s former senior platform manager. “A place to be yourself and share life with close friends and family. The personal network doesn’t replace your existing social networks – it augments them.”

“No following, no friending, just sharing with the people who matter most,” he said.

Why just 50? Morin said it has to do with what’s known as “Dunbar’s number,” based on research from Robin Dunbar, Oxford professor of evolutionary psychology, who suggested “150 is the maximum number of social relationships that the human brain can sustain at any given time.”

“Dunbar’s research also shows that personal relationships tend to expand in factors of roughly three. So while we may have five people whom we consider to be our closest friends, and 20 whom we maintain regular contact with, 50 is roughly the outer boundary of our personal networks.”